The present invention relates to a digital copier system of the type converting a document image to an electric signal and reproducing it with an image forming device and, more particularly, to a digital copier system wherein a plurality of applications share resources.
Generally, a digital copier of the type described transforms a document image to an electric signal executes various kinds of image processing with the electric signal, or image signal, and then causes an image forming device to reproduce the document image represented by the processed image signal. This type of copier can be provided with various kinds of applications. e.g., facsimile application, printer application, scanner application, and file system application. Then, the applications will share the resources available in the copier, e.g., image reading device, image forming device, operation and display panel, memory, and peripheral units. The peripheral units include a document feeder (DF) and a sorter.
However, the problem with the digital copier described above is that it is implemented as a single task system wherein a plurality of applications share the resources. This kind of system prevents a plurality of users to use the applications at the same time. For example, when a person is operating the copier to produce copies, another person cannot use the printer application unless the person waits until the copying operation has been completed or interrupted. While only the printer application is in use, facsimile transmission using the facsimile application cannot be effected until the printer output has been completed or interrupted, despite that the facsimile application is capable of sending facsimile data by using the image reading device.
In light of this, there has been proposed a multitask type digital copier system which allows the copier, printer, facsimile and other applications to share and selectively use the image reading device, image forming device and other resources.
Assume that a digital copier of the type described includes a duplex copy unit capable of turning over a paper to which an image has been transferred from a photoconductive element included in, for example, an electrophotographic image forming device, and again feeding it to the photoconductive element. With the duplex copy unit, it is possible to form an image on both sides of a single paper. The duplex copy unit is also shared by the applications. However, the problem is that the decision as to whether or not the duplex copy unit is usable differs from one application to another, preventing the system from having consistency.